314 The Philippine Journal of Science 1922 
navel orange being intermediate both in injection pressure and 
canker resistance. The comparisons of the average injection 
pressures thus apparently indicate that injection pressure is an 
approximate index of resistance to citrus canker. The work 
was then repeated, substituting an infusion of Pseudomonas citri 
for the water-bath immersion. 
INJECTION TESTS WITH INFUSION OF PSEUDOMONAS CITRI 
In the following experiments young, actively growing leaves 
were used of such condition as to be judged readily susceptible 
to infection with Pseudomonas citri. The leaves were in all 
cases on mature orchard trees, growing under identical envi- 
ronmental conditions. 
The infusion used was made from cultures of Pseudomonas 
citri on potato plugs. The cultures used were of the same 
age, and in comparative tests the same infusion was used. The 
temperature of the infusion during the experiment varied be- 
tween 28° and 31° C. 
In a few cases, cankers developed at the point of contact of 
the injector with the leaf. These cankers were recorded as at 
wounds. The cankers not so noted were on apparently unin- 
jured parts of the leaves and at a distance from the point of 
injector contact. 
The experimental results are presented in Tables 2, 3, and 4. . 
TABLE 2.—Showing the results of immersing leaves of the Szinkom man- 
darin orange in an infusion of Pseudomonas citri and exerting grad- 
uated degrees of pressure upon such leaves. 
—_ tw ee Incuba- 
cury & No.| geom tip Condition of leaves. Mar m Cankers. 
column. of twig. period. 
om, Days. 
0.0 4 8 | Full grown___-_--- ABs. 11 | None. 
0.0 4 : ees Wee Bt ee a a li Do. 
0.0 4 Visa ae age ie Se cn ke ae ii Do. 
0.0 6 » oes es gael beduucwemeceeawe lu Do. 
0.0 8 f 1 Malt orown 5 eee Bi Do. 
0,0 8 2 | Two-thirds grown_.------.---------------- 11 Do. 
0.0 8 ON DELS aa Se Ree a eee SCS RO aa 11 | 18 
0.0 11 TT One-fourtli gr0@ i... 02 conn nen nowt woos 26 {1 
0.0 il 2 | Half grown oe cies Re he ee 26/)1 
0.0 ll 3g eee Bgieo eect ot Saar Bie tere 26) 4 
2.4 3 i ane ae 1. 
2.5 1 1 | Two-thirds grown. sie 11 | None. 
2.5 1 AO eect ae eee i Do. 
2.8 9 41 Pwotinrdwervown. -..25-22-2.2-22- 2. -2225- 26 15> 
® Infection at evident wound. 
b Character of infection suggests wounds. 
